Introduce concept of global and individual output data retention
This is a new concept allowing the user to specifiy properties of a display
model (in best case identified by its EDID) on a global level.
This means independent of the setup/configuration of displays the display
model is part of its global properties are preserved.
The properties are for now:
- scale factor,
- refresh rate.
While redefining global values is possible at any time, user is also able to
specify for individual configurations special settings deviating from the
Test Plan: Manually. Autotest broken due to altered behavior.
Reviewers: Plasma, mart
Reviewed By: Plasma, mart
Maniphest Tasks: T10028
Differential Revision: https://phabricator.kde.org/D16991